Squirrels are biopolymers consisting of α-amino acid residues connected to each other by peptide bonds (-CO-NH-). Proteins are part of the cells and tissues of all living organisms. Protein molecules contain 20 residues of various amino acids.

Protein structure

Proteins have an inexhaustible variety of structures.

Primary protein structure is a sequence of amino acid units in a linear polypeptide chain.

Secondary structure is a spatial configuration of a protein molecule, reminiscent of a helix, which is formed as a result of twisting of the polypeptide chain due to hydrogen bonds between the groups: CO and NH.

Tertiary structure- this is the spatial configuration that a polypeptide chain twisted into a spiral takes on.

Quaternary structure- These are polymer formations from several protein macromolecules.

Physical properties

The properties that proteins perform are very diverse. Some proteins dissolve in water, usually forming colloidal solutions (for example, egg white); others dissolve in dilute salt solutions; still others are insoluble (for example, proteins of integumentary tissues).

Chemical properties

Denaturation– destruction of the secondary, tertiary structure of the protein under the influence of various factors: temperature, the action of acids, salts of heavy metals, alcohols, etc.

During denaturation under the influence of external factors (temperature, mechanical stress, the action of chemical agents and other factors), a change occurs in the secondary, tertiary and quaternary structures of the protein macromolecule, that is, its native spatial structure. The primary structure, and therefore the chemical composition of the protein, does not change. Physical properties change: solubility and ability to hydrate decrease, biological activity is lost. The shape of the protein macromolecule changes and aggregation occurs. At the same time, the activity of some groups increases, the effect of proteolytic enzymes on proteins is facilitated, and, therefore, it is more easily hydrolyzed.

In food technology, thermal denaturation of proteins is of particular practical importance, the degree of which depends on temperature, duration of heating and humidity. This must be remembered when developing heat treatment regimes for food raw materials, semi-finished products, and sometimes finished products. Thermal denaturation processes play a special role in blanching plant materials, drying grain, baking bread, and producing pasta. Protein denaturation can also be caused by mechanical action (pressure, rubbing, shaking, ultrasound). Protein denaturation is caused by the action of chemical reagents (acids, alkalis, alcohol, acetone). All these techniques are widely used in food and biotechnology.

Qualitative reactions to proteins:

a) When the protein burns, it smells like burnt feathers.

b) Protein +HNO 3 → yellow color

c) Protein solution + NaOH + CuSO 4 → purple color

Hydrolysis

Protein + H 2 O → mixture of amino acids

Functions of proteins in nature:

· catalytic (enzymes);

· regulatory (hormones);

· structural (wool keratin, silk fibroin, collagen);

motor (actin, myosin);

transport (hemoglobin);

· spare (casein, egg albumin);

· protective (immunoglobulins), etc.

Hydration

The process of hydration means the binding of water by proteins, and they exhibit hydrophilic properties: they swell, their mass and volume increase. The swelling of the protein is accompanied by its partial dissolution. The hydrophilicity of individual proteins depends on their structure. The hydrophilic amide (–CO–NH–, peptide bond), amine (NH 2) and carboxyl (COOH) groups present in the composition and located on the surface of the protein macromolecule attract water molecules, strictly orienting them to the surface of the molecule. By surrounding protein globules, a hydration (aqueous) shell prevents the stability of protein solutions. At the isoelectric point, proteins have the least ability to bind water; the hydration shell around protein molecules is destroyed, so they combine to form large aggregates. Aggregation of protein molecules also occurs when they are dehydrated using certain organic solvents, such as ethyl alcohol. This leads to the precipitation of proteins. When the pH of the environment changes, the protein macromolecule becomes charged and its hydration capacity changes.

With limited swelling, concentrated protein solutions form complex systems called jellies. Jellies are not fluid, elastic, have plasticity, a certain mechanical strength, and are able to retain their shape. Globular proteins can be completely hydrated, dissolving in water (for example, milk proteins), forming solutions with low concentrations. The hydrophilic properties of proteins are of great importance in biology and the food industry. A very mobile jelly, built mainly from protein molecules, is the cytoplasm - the semi-liquid contents of the cell. Highly hydrated jelly is raw gluten isolated from wheat dough, it contains up to 65% water. Hydrophilicity, the main quality of wheat grain, grain proteins and flour, plays a big role in the storage and processing of grain, and in baking. The dough, which is obtained in bakery production, is a protein swollen in water, a concentrated jelly containing starch grains.

Foaming

The foaming process is the ability of proteins to form highly concentrated liquid-gas systems called foams. The stability of foam, in which protein is a foaming agent, depends not only on its nature and concentration, but also on temperature. Proteins are widely used as foaming agents in the confectionery industry (marshmallows, marshmallows, souffles). Bread has a foam structure, and this affects its taste properties.

Combustion

Proteins burn to produce nitrogen, carbon dioxide and water, as well as some other substances. Combustion is accompanied by the characteristic smell of burnt feathers.

Color reactions.

• Xanthoprotein – interaction of aromatic and heteroatomic cycles in a protein molecule with concentrated nitric acid occurs, accompanied by the appearance of a yellow color;
• Biuret - weakly alkaline solutions of proteins interact with a solution of copper(II) sulfate to form complex compounds between Cu 2+ ions and polypeptides. The reaction is accompanied by the appearance of a violet-blue color;
• When proteins are heated with alkali in the presence of lead salts, a black precipitate that contains sulfur precipitates.



Squirrels- high-molecular organic compounds consisting of amino acid residues connected in a long chain by peptide bonds.

The composition of proteins in living organisms includes only 20 types of amino acids, all of which are alpha amino acids, and the amino acid composition of proteins and their order of connection with each other are determined by the individual genetic code of a living organism.

One of the features of proteins is their ability to spontaneously form spatial structures characteristic only of this particular protein.

Due to the specificity of their structure, proteins can have a variety of properties. For example, proteins with a globular quaternary structure, in particular chicken egg white, dissolve in water to form colloidal solutions. Proteins with a fibrillar quaternary structure do not dissolve in water. Fibrillar proteins, in particular, form nails, hair, and cartilage.

Chemical properties of proteins

Hydrolysis

All proteins are capable of undergoing hydrolysis reactions. In the case of complete hydrolysis of proteins, a mixture of α-amino acids is formed:

Protein + nH 2 O => mixture of α-amino acids

Denaturation

The destruction of the secondary, tertiary and quaternary structures of a protein without destroying its primary structure is called denaturation. Protein denaturation can occur under the influence of solutions of sodium, potassium or ammonium salts - such denaturation is reversible:

Denaturation occurring under the influence of radiation (for example, heating) or treatment of the protein with salts of heavy metals is irreversible:

For example, irreversible protein denaturation is observed during heat treatment of eggs during their preparation. As a result of denaturation of egg white, its ability to dissolve in water to form a colloidal solution disappears.

Qualitative reactions to proteins

Biuret reaction

If a 10% sodium hydroxide solution is added to a solution containing protein, and then a small amount of a 1% copper sulfate solution, a violet color will appear.

protein solution + NaOH (10% solution) + CuSO 4 = purple color

Xanthoprotein reaction

Protein solutions turn yellow when boiled with concentrated nitric acid:

protein solution + HNO 3 (conc.) => yellow color

Biological functions of proteins

catalytic	accelerate various chemical reactions in living organisms	enzymes
structural	cell building material	collagen, cell membrane proteins
protective	protect the body from infections	immunoglobulins, interferon
regulatory	regulate metabolic processes	hormones
transport	transfer of vital substances from one part of the body to another	hemoglobin carries oxygen
energy	supply the body with energy	1 gram of protein can provide the body with 17.6 J of energy
motor (motor)	any motor functions of the body	myosin (muscle protein)

Squirrels- high molecular weight organic compounds consisting of α-amino acid residues.

IN protein composition includes carbon, hydrogen, nitrogen, oxygen, sulfur. Some proteins form complexes with other molecules containing phosphorus, iron, zinc and copper.

Proteins have a large molecular weight: egg albumin - 36,000, hemoglobin - 152,000, myosin - 500,000. For comparison: the molecular weight of alcohol is 46, acetic acid - 60, benzene - 78.

Amino acid composition of proteins

Squirrels- non-periodic polymers, the monomers of which are α-amino acids. Typically, 20 types of α-amino acids are called protein monomers, although over 170 of them are found in cells and tissues.

Depending on whether amino acids can be synthesized in the body of humans and other animals, they are distinguished: nonessential amino acids- can be synthesized; essential amino acids- cannot be synthesized. Essential amino acids must be supplied to the body through food. Plants synthesize all types of amino acids.

Depending on the amino acid composition, proteins are: complete- contain the entire set of amino acids; defective- some amino acids are missing in their composition. If proteins consist only of amino acids, they are called simple. If proteins contain, in addition to amino acids, a non-amino acid component (prosthetic group), they are called complex. The prosthetic group can be represented by metals (metalloproteins), carbohydrates (glycoproteins), lipids (lipoproteins), nucleic acids (nucleoproteins).

All amino acids contain: 1) carboxyl group (-COOH), 2) amino group (-NH 2), 3) radical or R-group (the rest of the molecule). The structure of the radical is different for different types of amino acids. Depending on the number of amino groups and carboxyl groups included in the composition of amino acids, they are distinguished: neutral amino acids having one carboxyl group and one amino group; basic amino acids having more than one amino group; acidic amino acids having more than one carboxyl group.

Amino acids are amphoteric compounds, since in solution they can act as both acids and bases. In aqueous solutions, amino acids exist in different ionic forms.

Peptide bond

Peptides- organic substances consisting of amino acid residues connected by peptide bonds.

The formation of peptides occurs as a result of the condensation reaction of amino acids. When the amino group of one amino acid interacts with the carboxyl group of another, a covalent nitrogen-carbon bond occurs between them, which is called peptide. Depending on the number of amino acid residues included in the peptide, there are dipeptides, tripeptides, tetrapeptides etc. The formation of a peptide bond can be repeated many times. This leads to the formation polypeptides. At one end of the peptide there is a free amino group (called the N-terminus), and at the other there is a free carboxyl group (called the C-terminus).

Spatial organization of protein molecules

The performance of certain specific functions by proteins depends on the spatial configuration of their molecules; in addition, it is energetically unfavorable for the cell to keep proteins in an unfolded form, in the form of a chain, therefore polypeptide chains undergo folding, acquiring a certain three-dimensional structure, or conformation. There are 4 levels spatial organization of proteins.

Primary protein structure- the sequence of arrangement of amino acid residues in the polypeptide chain that makes up the protein molecule. The bond between amino acids is a peptide bond.

If a protein molecule consists of only 10 amino acid residues, then the number of theoretically possible variants of protein molecules that differ in the order of alternation of amino acids is 10 20. Having 20 amino acids, you can make even more diverse combinations from them. About ten thousand different proteins have been found in the human body, which differ both from each other and from the proteins of other organisms.

It is the primary structure of the protein molecule that determines the properties of the protein molecules and its spatial configuration. Replacing just one amino acid with another in a polypeptide chain leads to a change in the properties and functions of the protein. For example, replacing the sixth glutamic amino acid in the β-subunit of hemoglobin with valine leads to the fact that the hemoglobin molecule as a whole cannot perform its main function - oxygen transport; In such cases, the person develops a disease called sickle cell anemia.

Secondary structure- ordered folding of the polypeptide chain into a spiral (looks like an extended spring). The turns of the helix are strengthened by hydrogen bonds that arise between carboxyl groups and amino groups. Almost all CO and NH groups take part in the formation of hydrogen bonds. They are weaker than peptide ones, but, repeated many times, impart stability and rigidity to this configuration. At the level of secondary structure, there are proteins: fibroin (silk, spider web), keratin (hair, nails), collagen (tendons).

Tertiary structure- packing of polypeptide chains into globules, resulting from the formation of chemical bonds (hydrogen, ionic, disulfide) and the establishment of hydrophobic interactions between the radicals of amino acid residues. The main role in the formation of the tertiary structure is played by hydrophilic-hydrophobic interactions. In aqueous solutions, hydrophobic radicals tend to hide from water, grouping inside the globule, while hydrophilic radicals, as a result of hydration (interaction with water dipoles), tend to appear on the surface of the molecule. In some proteins, the tertiary structure is stabilized by disulfide covalent bonds formed between the sulfur atoms of two cysteine ​​residues. At the tertiary structure level there are enzymes, antibodies, and some hormones.

Quaternary structure characteristic of complex proteins whose molecules are formed by two or more globules. The subunits are held in the molecule by ionic, hydrophobic, and electrostatic interactions. Sometimes, during the formation of a quaternary structure, disulfide bonds occur between subunits. The most studied protein with a quaternary structure is hemoglobin. It is formed by two α-subunits (141 amino acid residues) and two β-subunits (146 amino acid residues). Associated with each subunit is a heme molecule containing iron.

If for some reason the spatial conformation of proteins deviates from normal, the protein cannot perform its functions. For example, the cause of “mad cow disease” (spongiform encephalopathy) is the abnormal conformation of prions, the surface proteins of nerve cells.

Properties of proteins

The amino acid composition and structure of the protein molecule determine it properties. Proteins combine basic and acidic properties, determined by amino acid radicals: the more acidic amino acids in a protein, the more pronounced its acidic properties. The ability to donate and add H + is determined buffering properties of proteins; One of the most powerful buffers is hemoglobin in red blood cells, which maintains blood pH at a constant level. There are soluble proteins (fibrinogen), and there are insoluble proteins that perform mechanical functions (fibroin, keratin, collagen). There are proteins that are chemically active (enzymes), there are chemically inactive proteins that are resistant to various environmental conditions and those that are extremely unstable.

External factors (heat, ultraviolet radiation, heavy metals and their salts, pH changes, radiation, dehydration)

can cause disruption of the structural organization of the protein molecule. The process of loss of the three-dimensional conformation inherent in a given protein molecule is called denaturation. The cause of denaturation is the breaking of bonds that stabilize a certain protein structure. Initially, the weakest ties are broken, and as conditions become stricter, even stronger ones are broken. Therefore, first the quaternary, then the tertiary and secondary structures are lost. A change in spatial configuration leads to a change in the properties of the protein and, as a result, makes it impossible for the protein to perform its inherent biological functions. If denaturation is not accompanied by destruction of the primary structure, then it may be reversible, in this case, self-recovery of the conformation characteristic of the protein occurs. For example, membrane receptor proteins undergo such denaturation. The process of restoring protein structure after denaturation is called renaturation. If restoration of the spatial configuration of the protein is impossible, then denaturation is called irreversible.

Functions of proteins

Function	Examples and explanations
Construction	Proteins are involved in the formation of cellular and extracellular structures: they are part of cell membranes (lipoproteins, glycoproteins), hair (keratin), tendons (collagen), etc.
Transport	The blood protein hemoglobin attaches oxygen and transports it from the lungs to all tissues and organs, and from them transfers carbon dioxide to the lungs; The composition of cell membranes includes special proteins that ensure the active and strictly selective transfer of certain substances and ions from the cell to the external environment and back.
Regulatory	Protein hormones take part in the regulation of metabolic processes. For example, the hormone insulin regulates blood glucose levels, promotes glycogen synthesis, and increases the formation of fats from carbohydrates.
Protective	In response to the penetration of foreign proteins or microorganisms (antigens) into the body, special proteins are formed - antibodies that can bind and neutralize them. Fibrin, formed from fibrinogen, helps stop bleeding.
Motor	The contractile proteins actin and myosin provide muscle contraction in multicellular animals.
Signal	Built into the surface membrane of the cell are protein molecules that are capable of changing their tertiary structure in response to environmental factors, thus receiving signals from the external environment and transmitting commands to the cell.
Storage	In the body of animals, proteins, as a rule, are not stored, with the exception of egg albumin and milk casein. But thanks to proteins, some substances can be stored in the body; for example, during the breakdown of hemoglobin, iron is not removed from the body, but is stored, forming a complex with the protein ferritin.
Energy	When 1 g of protein breaks down into final products, 17.6 kJ is released. First, proteins break down into amino acids, and then into the final products - water, carbon dioxide and ammonia. However, proteins are used as a source of energy only when other sources (carbohydrates and fats) are used up.
Catalytic	One of the most important functions of proteins. Provided by proteins - enzymes that accelerate biochemical reactions occurring in cells. For example, ribulose biphosphate carboxylase catalyzes the fixation of CO 2 during photosynthesis.

Enzymes

Enzymes, or enzymes, are a special class of proteins that are biological catalysts. Thanks to enzymes, biochemical reactions occur at tremendous speed. The speed of enzymatic reactions is tens of thousands of times (and sometimes millions) higher than the speed of reactions occurring with the participation of inorganic catalysts. The substance on which the enzyme acts is called substrate.

Enzymes are globular proteins, structural features enzymes can be divided into two groups: simple and complex. Simple enzymes are simple proteins, i.e. consist only of amino acids. Complex enzymes are complex proteins, i.e. In addition to the protein part, they contain a group of non-protein nature - cofactor. Some enzymes use vitamins as cofactors. The enzyme molecule contains a special part called the active center. Active center- a small section of the enzyme (from three to twelve amino acid residues), where the binding of the substrate or substrates occurs to form an enzyme-substrate complex. Upon completion of the reaction, the enzyme-substrate complex breaks down into the enzyme and the reaction product(s). Some enzymes have (except active) allosteric centers- areas to which enzyme speed regulators are attached ( allosteric enzymes).

Reactions of enzymatic catalysis are characterized by: 1) high efficiency, 2) strict selectivity and direction of action, 3) substrate specificity, 4) fine and precise regulation. The substrate and reaction specificity of enzymatic catalysis reactions are explained by the hypotheses of E. Fischer (1890) and D. Koshland (1959).

E. Fischer (key-lock hypothesis) suggested that the spatial configurations of the active center of the enzyme and the substrate must correspond exactly to each other. The substrate is compared to the “key”, the enzyme to the “lock”.

D. Koshland (hand-glove hypothesis) suggested that the spatial correspondence between the structure of the substrate and the active center of the enzyme is created only at the moment of their interaction with each other. This hypothesis is also called induced correspondence hypothesis.

The rate of enzymatic reactions depends on: 1) temperature, 2) enzyme concentration, 3) substrate concentration, 4) pH. It should be emphasized that since enzymes are proteins, their activity is highest under physiologically normal conditions.

Most enzymes can only work at temperatures between 0 and 40°C. Within these limits, the reaction rate increases approximately 2 times with every 10 °C increase in temperature. At temperatures above 40 °C, the protein undergoes denaturation and enzyme activity decreases. At temperatures close to freezing, enzymes are inactivated.

As the amount of substrate increases, the rate of the enzymatic reaction increases until the number of substrate molecules equals the number of enzyme molecules. With a further increase in the amount of substrate, the speed will not increase, since the active centers of the enzyme are saturated. An increase in enzyme concentration leads to increased catalytic activity, since a larger number of substrate molecules undergo transformations per unit time.

For each enzyme, there is an optimal pH value at which it exhibits maximum activity (pepsin - 2.0, salivary amylase - 6.8, pancreatic lipase - 9.0). At higher or lower pH values, enzyme activity decreases. With sudden changes in pH, the enzyme denatures.

The speed of allosteric enzymes is regulated by substances that attach to allosteric centers. If these substances speed up a reaction, they are called activators, if they slow down - inhibitors.

Classification of enzymes

Based on the type of chemical transformations they catalyze, enzymes are divided into 6 classes:

1. oxireductases(transfer of hydrogen, oxygen or electron atoms from one substance to another - dehydrogenase),
2. transferases(transfer of methyl, acyl, phosphate or amino group from one substance to another - transaminase),
3. hydrolases(hydrolysis reactions in which two products are formed from the substrate - amylase, lipase),
4. lyases(non-hydrolytic addition to the substrate or detachment of a group of atoms from it, in which case C-C, C-N, C-O, C-S bonds can be broken - decarboxylase),
5. isomerases(intramolecular rearrangement - isomerase),
6. ligases(the connection of two molecules as a result of the formation of C-C, C-N, C-O, C-S bonds - synthetase).

Classes are in turn subdivided into subclasses and subsubclasses. In the current international classification, each enzyme has a specific code, consisting of four numbers separated by dots. The first number is the class, the second is the subclass, the third is the subsubclass, the fourth is the serial number of the enzyme in this subclass, for example, the arginase code is 3.5.3.1.

Go to lectures No. 2"Structure and functions of carbohydrates and lipids"

Go to lectures No. 4"Structure and functions of ATP nucleic acids"

Before talking about the most important physical and chemical properties of protein, you need to know what it consists of and what its structure is. Proteins are an important natural biopolymer; amino acids serve as the foundation for them.

What are amino acids

These are organic compounds that contain carboxyl and amine groups. Thanks to the first group they have carbon, oxygen and hydrogen, and the other - nitrogen and hydrogen. Alpha amino acids are considered the most important because they are needed for the formation of proteins.

There are essential amino acids called proteinogenic amino acids. So they are responsible for the appearance of proteins. There are only 20 of them, but they can form countless protein compounds. However, none of them will be completely identical to the other. This is possible thanks to the combinations of elements that are found in these amino acids.

Their synthesis does not occur in the body. Therefore, they get there along with food. If a person receives them in insufficient quantities, then the normal functioning of various systems may be disrupted. Proteins are formed through a polycondensation reaction.

Proteins and their structure

Before moving on to the physical properties of proteins, it is worth giving a more precise definition of this organic compound. Proteins are one of the most significant bioorganic compounds that are formed due to amino acids and take part in many processes occurring in the body.

The structure of these compounds depends on the order in which amino acid residues alternate. As a result, it looks like this:

• primary (linear);
• secondary (spiral);
• tertiary (globular).

Their classification

Due to the huge variety of protein compounds and the varying degrees of complexity of their composition and different structures, for convenience, there are classifications that rely on these characteristics.

Their composition is as follows:

• simple;
• complex, which are in turn divided into:

1. combination of protein and carbohydrates;
2. combination of proteins and fats;
3. connection of protein molecules and nucleic acids.

By solubility:

• water soluble;
• fat-soluble.

A short description of protein compounds

Before moving on to the physical and chemical properties of proteins, it will be useful to give them a little characterization. Of course, their properties are important for the normal functioning of a living organism. In their original state, these are solid substances that either dissolve in various liquids or not.

Briefly speaking about the physical properties of proteins, then they determine many of the most important biological processes in the body. For example, such as transport of substances, construction function, etc. The physical properties of proteins depend on whether they are soluble or not. It is these features that will be written about further.

Physical properties of proteins

It has already been written above about their state of aggregation and solubility. Therefore, we move on to the following properties:

1. They have a large molecular weight, which depends on certain environmental conditions.
2. Their solubility has a wide range, as a result of which electrophoresis, a method by which proteins are isolated from mixtures, becomes possible.

Chemical properties of protein compounds

Readers now know what physical properties proteins have. Now we need to talk about equally important chemical ones. They are listed below:

1. Denaturation. Protein coagulation under the influence of high temperatures, strong acids or alkalis. During denaturation, only the primary structure is preserved, and all biological properties of proteins are lost.
2. Hydrolysis. As a result, simple proteins and amino acids are formed, because the primary structure is destroyed. It is the basis of the digestion process.
3. Qualitative reactions for protein determination. There are only two of them, and the third is needed in order to detect sulfur in these compounds.
4. Biuret reaction. Proteins are exposed to copper hydroxide precipitate. The result is a purple coloration.
5. Xanthoprotein reaction. The effect is carried out using concentrated nitric acid. This reaction results in a white precipitate that turns yellow when heated. And if you add an aqueous ammonia solution, an orange color appears.
6. Determination of sulfur in proteins. When the proteins burn, the smell of “burnt horn” begins to be felt. This phenomenon is explained by the fact that they contain sulfur.

So these were all the physical and chemical properties of proteins. But, of course, it is not only because of them that they are considered the most important components of a living organism. They determine the most important biological functions.

Biological properties of proteins

We examined the physical properties of proteins in chemistry. But it’s also worth talking about the impact they have on the body and why it won’t function fully without them. The following are the functions of proteins:

1. enzymatic. Most reactions in the body occur with the participation of enzymes that are of protein origin;
2. transport. These elements deliver other important molecules to tissues and organs. One of the most important transport proteins is hemoglobin;
3. structural. Proteins are the main building material for many tissues (muscle, integumentary, supporting);
4. protective. Antibodies and antitoxins are a special type of protein compounds that form the basis of immunity;
5. signal The receptors that are responsible for the functioning of the sense organs also have proteins in their structure;
6. storing. This function is performed by special proteins, which can be building materials and sources of additional energy during the development of new organisms.

Proteins can be converted into fats and carbohydrates. But they will not be able to become squirrels. Therefore, the lack of these particular compounds is especially dangerous for a living organism. The energy released is small and is inferior in this regard to fats and carbohydrates. However, they are the source of essential amino acids in the body.

How to understand that there is not enough protein in the body? A person’s health deteriorates, rapid exhaustion and fatigue sets in. Excellent sources of protein are various varieties of wheat, meat and fish products, dairy products, eggs and some types of legumes.

It is important to know not only the physical properties of proteins, but also the chemical ones, as well as what significance they have for the body from a biological point of view. Protein compounds are unique in that they are sources of essential amino acids that are necessary for the normal functioning of the human body.

Squirrels- natural polypeptides with a huge molecular weight. They are part of all living organisms and perform various biological functions.

Protein structure.

Proteins have 4 levels of structure:

• protein primary structure- linear sequence of amino acids in a polypeptide chain, folded in space:

• protein secondary structure- conformation of the polypeptide chain, because twisting in space due to hydrogen bonds between N.H. And CO groups. There are 2 installation methods: α -spiral and β - structure.

• protein tertiary structure is a three-dimensional representation of a swirling α -spiral or β -structures in space:

This structure is formed by -S-S- disulfide bridges between cysteine ​​residues. Oppositely charged ions participate in the formation of such a structure.

• protein quaternary structure is formed due to the interaction between different polypeptide chains:

Protein synthesis.

The synthesis is based on a solid-phase method, in which the first amino acid is fixed on a polymer carrier, and new amino acids are sequentially attached to it. The polymer is then separated from the polypeptide chain.

Physical properties of protein.

The physical properties of a protein are determined by its structure, so proteins are divided into globular(soluble in water) and fibrillar(insoluble in water).

Chemical properties of proteins.

1. Protein Denaturation(destruction of the secondary and tertiary structure while maintaining the primary). An example of denaturation is the coagulation of egg whites when eggs are boiled.

2. Protein hydrolysis- irreversible destruction of the primary structure in an acidic or alkaline solution with the formation of amino acids. This way you can determine the quantitative composition of proteins.

3. Qualitative reactions:

Biuret reaction- interaction of the peptide bond and copper (II) salts in an alkaline solution. At the end of the reaction, the solution turns purple.

Xanthoprotein reaction- when reacting with nitric acid, a yellow color is observed.

Biological significance of protein.

1. Proteins are a building material; muscles, bones, and tissues are built from it.

2. Proteins - receptors. They transmit and perceive signals coming from neighboring cells from the environment.

3. Proteins play an important role in the body's immune system.

4. Proteins perform transport functions and transport molecules or ions to the site of synthesis or accumulation. (Hemoglobin carries oxygen to tissues.)

5. Proteins - catalysts - enzymes. These are very powerful selective catalysts that speed up reactions millions of times.

There are a number of amino acids that cannot be synthesized in the body - irreplaceable, they are obtained only from food: tisine, phenylalanine, methinine, valine, leucine, tryptophan, isoleucine, threonine.